How to enable X-forwarding in the OpenSSH server

[joukj]

Hi All,

I do on my linux system: ssh -Y openvms-machine

With HP TCP/IP services I always got an X-display to tunnel X through ssh defined on the OpenVMS machine,
With OpenSSH(AXP, Itanium & X86) I get "X11 forwarding request failed on channel 0" just after the connection is made and of course no display available in OpenVMS.
I set X11Forwarding=yes in ssh_configd,

Now I have no Idea how to get the x-forwarding working.

Regards
Jouk

[babydr]

@Joukl , Try looking for a logical name that has X11.*offset sort of name . Somehow it appears that the present server thinks it has to offset the Display by '0' (Zero) which is ALWAYS the local primary display device .
Hth , JimL

[joukj]

In the configuration file there are 2 options "X11DisplayOffset 10" and "X11UseLocalHost yes". So the dedaults look OK. Even uncommenting them and defining them explicitly does not help.

[mike632t]

"X11 forwarding request failed on channel 0"

Does anyone know how to resolve this problem?

I can use X11 forwarding when connecting to another Linux system, but I'm getting exactly the same error when I try to use X11 forwarding when connecting to an Open VMS E9.2-1 system using OpenSSH.

Code: Select all

$ ssh -vv -X vmsuser@192.168.0.42
OpenSSH_9.2p1 Debian-2+deb12u1, OpenSSL 3.0.11 19 Sep 2023
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: include /etc/ssh/ssh_config.d/*.conf matched no files
  ;
  ;
  ;
debug1: Authentications that can continue: publickey,password,keyboard-interactive
debug2: we did not send a packet, disable method
debug1: Next authentication method: password
vmsuser@192.168.0.42's password: PASSWORD
debug2: we sent a password packet, wait for reply
Authenticated to 192.168.0.42 ([192.168.0.42]:22) using "password".
debug1: channel 0: new session [client-session] (inactive timeout: 0)
  :
  :
  :
debug1: Remote: No xauth program; cannot forward X11.
debug2: channel_input_status_confirm: type 100 id 0
X11 forwarding request failed on channel 0
  :
  :
  :
debug2: shell request accepted on channel 0

    This is node VMS092, running VMS E9.2-1  
    Last interactive login on Sunday,  5-NOV-2023 23:29:56.31
    Last non-interactive login on Sunday,  5-NOV-2023 20:52:02.65

$ SHOW DISPLAY
%DECW-W-OPENIN, error opening DECW$DISPLAY as input
-SYSTEM-W-NOSUCHDEV, no such device available
$ 

I have noticed that I get one login failure just before I enter the vmsuser's password, but I think this is normal as I'm not using a preshared key to authenticate.

I suspect that the client is trying to tell me that xauth is not installed or not running on VMS092?

Updated : 6/11

I have tried to use the instructons here but without success ("X11 forwarding request failed on channel 0").

[dmjb]

VSI have stated that X forwarding is not supported in OpenSSH on VMS. I don't remember if this only applies to x86, or if it applies to OpenSSH on Alpha and IA64 as well.

[imiller]

recently on comp.os.vms https://groups.google.com/g/comp.os.vms ... QNvQkEBAAJ Rob Brooks posted

The VMS port by VSI of OpenSSH does not yet support X port forwarding.

It's coming soon.

--
-- Rob

[mike632t]

I'd seen the posts that said that X11 forwarding wasn't supported/working (yet), but the linked post here seems to suggest that there is a work around.

I think the commands the post suggests are as follows, first connect to the VMS system using the '-R' option to redirect any connections to port 6000 on the (VMS) host to port 6000 on the localhost.

Code: Select all

$ ssh -R 6000:127.0.0.1:6000 user@vms92

Then login and create a display on the VMS system using 127.0.0.1 (this should default to using port 6000, which will be (reverse) forwarded to port 6000 on the localhost).

Code: Select all

$ SET DISPLAY/CREATE/TRANSPORT=TCPIP/NODE=127.0.0.1
$ sh display

    Device:    WSA1:  [super]
    Node:      127.0.0.1
    Transport: TCPIP
    Server:    0
    Screen:    0
$

This makes sense in theory but I've obviously not got it quite right as I get the following error.

Code: Select all

$ RUN SYS$SYSTEM:DECW$CLOCK
connect_to 127.0.0.1 port 6000: failed.
XIO:  fatal IO error 65535 (network partner disconnected logical link) on X server "_WSA1:"
      after 0 requests (0 known processed) with 0 events remaining.
X Error of failed request:  BadConnection (fatal error on display connection)
  Major opcode of failed request:  1 (X_CreateWindow)
  Serial number of failed request:  0
  Current serial number in output stream:  0
%XLIB-E-ERROREVENT, error event received from server
Xlib: client uses different protocol version (11) than server (0)!
X Toolkit Error: Can't Open display
%DWT-F-NOMSG, Message number 03AB8204
$ 

[mike632t]

Found the missing piece of the puzzle!!! (It was obvious once I thought of it).
You need to allow inbound connections to the xserver from 127.0.0.1, before connecting using ssh.

Code: Select all

$ xhost +127.0.0.1